For many years voice telephone service was implemented over a circuit switched network commonly known as the public switched telephone network (PSTN) and controlled by a local telephone service provider. In such systems, the analog electrical signals representing the conversation are transmitted between the two telephone handsets on a dedicated twisted-pair-copper-wire circuit. More specifically, each of the two endpoint telephones is coupled to a local switching station by a dedicated pair of copper wires known as a subscriber loop. The two switching stations are connected by a trunk line network which in the early systems comprised multiple copper wire pairs. When a telephone call is placed, the circuit is completed by dynamically coupling each subscriber loop to the trunk line network such that a circuit is completed between the two subscriber loops.
More recently both the trunk lines between central offices and the subscriber loops have been replaced with digital transmission systems. More specifically, multiple twisted pair trunk lines have been replaced a high bandwidth transmission medium such as fiber optics and a computing device on each end of the transmission medium utilizes a time division protocol to create multiple 64 kb communication channels coupled to the other computing device. Each 64 kb “point-to-point” communication channel is adequate for emulating a twisted pair circuit for audio communication.
Similarly, businesses that utilize a private branch exchange (PBX) system for their internal telephone network often utilize one or more ISDN lines for coupling to the central office rather than multiple twisted pair subscriber loops. The PBX system and the corresponding systems of the central office utilize a time division protocol to creating multiple 64 Kb “point-to-point” communication channels and a signaling channel.
Unlike the “point-to-point dedicated channel” structure of the PSTN, the Internet transmits frames of digital date between two endpoints utilizing a frame switched protocol. The Internet comprises multiple routers interconnected to each other by broadband transmission mediums. Each data frame includes complete addressing information that enables it to be transferred from its origin endpoint to its destination endpoint by the routers and independent of any other data frames that may be addressed from the same origin endpoint to the same destination endpoint.
Advances in packet switched communication technologies, audio compression technologies, and Internet network capacity have made it possible for telephone calls to be provided over the packet switched structure of the Internet.
To enable Internet telephone service to interoperate with a customer's traditional PBX system and with the PSTN central office, Internet gateways have been developed. Referring to FIG. 1, The Internet gateway 10 is coupled to the customer's PBX 12 by one or more traditional ISDN lines 24a and 24b. The gateway 10 is also coupled to a PSTN central office by two or more traditional ISDN lines 18a and 18b and to the Internet by an Internet communication link 22.
The PBX manages a private network 14 that interconnects the PBX 12 to a plurality of telephones 16. In operation, when a call is placed outbound from the PBX 12, the IP gateway 10 selects whether to complete the call to its destination utilizing the PSTN or the Internet. When a call is placed on the PSTN to a telephone number associated with the all of the multiple ISDN lines 18a and 18b (e.g. a pilot number), the PSTN central office will hunt for an open channel first on line 18a and then on line 18b to complete the call. The PSTN central office will only return a busy signal to the caller if all of the open channels within the hunt group are in use. In turn, the gateway 10 will hunt for an open channel first on line 24a and then on line 24b to complete the call to the PBX 12.
A problem exists in that if several calls are in progress over the Internet, it is possible for all of the media channels on lines 24a and 24b to be in use while one or more of the media channels on lines 18a or 18b remain open. In which case, the central office will not provide the applicable busy signal to the caller, but instead will attempt to signal the call for one of the open media channels of lines 18a ore 18b. In this situation, the gateway 10 can not connect the call because the media channels of lines 24a and 24b are all in use. This situation can cause a hunt failure in which the PSTN central office will not hunt the failed channel for future calls. This is a problematic situation in that it disrupts the useful hunt function offered by telephone service providers.
As such, there exists a need for an Internet telephony gateway system that includes a mechanism for deactivating channels to the PSTN central office from time to time such that the PSTN central office does not attempt to hunt and complete calls on such deactivated channels and enable re-activating channels when the channels are available for hunting and completing calls.